Increased glutamic acid decarboxylase (GAD) mRNA and GAD activity in cerebellar Purkinje cells following lesion-induced increases in cell firing.

Lesions of the inferior olive-climbing fiber projection to the cerebellar Purkinje cell were produced in adult rats using the neurotoxin 3-acetylpyridine. At 7 days post-lesion, glutamic acid decarboxylase (GAD) activity in Purkinje cell axons terminating in the lateral division of the deep cerebellar nucleus was significantly increased (+58%) above control levels. GAD mRNA levels in Purkinje cell bodies from the same animals were measured by in situ hybridization histochemistry using a radiolabeled cRNA probe for GAD mRNA. GAD mRNA was significantly elevated (+42%) above control at 7 days post-lesion. Because lesions of the climbing fiber system increase Purkinje cell firing rates, the results suggest that increased Purkinje cell activity induces transcription of GAD mRNA, which in turn results in increased GAD availability in Purkinje cell terminals.